NiSe2-anchored N, S-doped graphene/Ni foam as a free-standing bifunctional electrocatalyst for efficient water splitting

A state-of-the-art review on biomass-derived carbon materials for supercapacitor applications: From precursor selection to design optimization

Biomass-derived carbon materials have the characteristics of a wide range of precursor sources, controllable carbon nano-dimension, large specific surface area and abundant heteroatoms doping. At present, biomass-derived carbon materials have been widely used in electrochemical energy storage devices, especially the research and development of biomass-derived carbon materials for supercapacitors has become mature and in-depth. Therefore, it is of importance to summarize the advanced technologies and strategies for optimizing biomass-derived carbon materials for supercapacitors, which will effectively promote the further development of high-performance supercapacitors. In this review, the recent research progress of biomass-derived carbon materials is provided in detail, including the selection of biomass precursors, the design of carbon nano-dimension and the theory of heteroatom doping. Besides, the preparation methods of biomass-derived carbon materials and the related processes of optimizing the electrochemical performance are also summarized. This review ends with the perspectives for future research directions and challenges in the field of biomass-derived carbon materials for electrochemical applications. This review aims to provide helpful reference information for the nano-dimensional design and electrochemical performance optimization of biomass-derived carbon materials for the practical application of supercapacitors.

Electronic structure engineering on NiSe2 micro-octahedra via nitrogen doping enabling long cycle life magnesium ion batteries

Multivalent ion batteries have attracted great attention because of their abundant reserves, low cost and high safety. Among them, magnesium ion batteries (MIBs) have been regarded as a promising alternative for large-scale energy storage device owing to its high volumetric capacities and unfavorable dendrite formation. However, the strong interaction between Mg²⁺ and electrolyte as well as cathode material results in very slow insertion and diffusion kinetics. Therefore, it is highly necessary to develop high-performance cathode materials compatible with electrolyte for MIBs. Herein, the electronic structure of NiSe₂ micro-octahedra was modulated by nitrogen doping (N-NiSe₂) through hydrothermal method followed by a pyrolysis process and this N-NiSe₂ micro-octahedra was used as cathode materials for MIBs. It is worth noting that N-NiSe₂ micro-octahedra shows more redox active sites and faster Mg²⁺ diffusion kinetics compared with NiSe₂ micro-octahedra without nitrogen doping. Moreover, the density functional theory (DFT) calculations indicated that the doping of nitrogen could improve the conductivity of active materials on the one hand, facilitating Mg²⁺ ion diffusion kinetics, and on the other hand, nitrogen dopant sites could provide more Mg²⁺ adsorption sites. As a result, the N-NiSe₂ micro-octahedra cathode exhibits a high reversible discharge capacity of 169 mAh g^-1 at the current density of 50 mA g^-1, and a good cycling stability over 500 cycles with a maintained discharge capacity of 158.5 mAh g^-1. This work provides a new idea to improve the electrochemical performance of cathode materials for MIBs by the introduction of heteroatom dopant.

Cuboid-like phosphorus-doped metal-organic framework-derived CoSe2 on carbon cloth as an advanced bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries

Zinc-air batteries (ZABs) are regarded as attractive devices for electrochemical energy storage and conversion due to their outstanding electrochemical performance, low price, and high safety. However, it remains a challenge to design a stable and efficient bifunctional oxygen catalyst that can accelerate the reaction kinetics and improve the performance of ZABs. Herein, a phosphorus-doped transition metal selenide/carbon composite catalyst derived from metal-organic frameworks (P-CoSe₂/C@CC) is constructed by a self-supporting carbon cloth structure through a simple solvothermal process with subsequent selenization and phosphatization. The P-CoSe₂/C@CC exhibits a low overpotential of 303.1 mV at 10 mA cm^-2 toward the oxygen evolution reaction and an obvious reduction peak for the oxygen reduction reaction. The abovementioned electrochemical performances for the P-CoSe₂/C@CC are attributed to the specific architecture, the super-hydrophilic surface, and the P-doping effect. Remarkably, the homemade zinc-air battery based on our P-CoSe₂/C@CC catalyst shows an expected peak power density of 124.4 mW cm^-2 along with excellent cycling stability, confirming its great potential application in ZABs for advanced bifunctional electrocatalysis.

Influence of Nitrogen-Doped Carbon Quantum Dots on the Electrocatalytic Performance of the CoP Nanoflower Catalyst for OER

Cobalt phosphides modified by nitrogen-doped carbon quantum dots (CoP-NCQDs) were successfully constructed by a facile and low-cost hydrothermal treatment, which is expected to replace traditional noble-metal oxygen evolution reaction electrode materials. Detailed experiments and findings show that nitrogen-doped carbon quantum dots (NCQDs) have a significant impact on the morphology of the CoP catalyst, and nitrogen doping can regulate the surface-active sites to obtain the catalyst with abundant structural defects. Simultaneously, nitrogen doping can regulate the content of pyridinic N and pyrrolic N, which exerts positive effects on the formation of the bond structure and electron conduction between NCQDs and CoP.

Tiny Ni Nanoparticles Embedded in Boron- and Nitrogen-Codoped Porous Carbon Nanowires for High-Efficiency Water Splitting

The integration of nickel (Ni) nanoparticle (NP)-embedded carbon layers (Ni@C) into the three-dimensional (3D) hierarchically porous carbon architectures, where ultrahigh boron (B) and nitrogen (N) doping is a potential methodology for boosting Ni catalysts' water splitting performances, was achieved. In this study, the novel 3D ultrafine Ni NP-embedded and B- and N-codoped hierarchically porous carbon nanowires (denoted as Ni@BNPCFs) were successfully synthesized via pyrolysis of the corresponding 3D nickel acetate [Ni(AC)₂·4H₂O]-hydroxybenzeneboronic acid-polyvinylpyrrolidone precursor networks woven by electrospinning. After optimizing the pyrolysis temperatures, various structural and morphological characterization analyses indicate that the optimal Ni@BNPCFs-900 networks own a large surface area, abundant micro/mesopores, and vast carbon edges/defects, which boost doping a large amount of B (5.81 atom %) and N (5.84 atom %) dopants into carbon frameworks with 6.36 atom % of BC₃, pyridinic-N (pyridinic-N-Ni), and graphitic-N active sites. Electrochemical measurements demonstrate that Ni@BNPCFs-900 reveals the best hydrogen evolution reaction (HER) and oxygen reduction reaction catalytic activities in an alkaline solution. The HER potential at 10 mA cm^-2 [E₁₀ = -164.2 mV vs reversible hydrogen electrode (RHE)] of the optimal Ni@BNPCFs-900 is just 96.2 mV more negative than that of the state-of-the-art 20 wt % Pt/C (E₁₀ = -68 mV vs RHE). In particular, the OER E₁₀ and Tafel slope of the optimal Ni@BNPCFs-900 (1.517 V vs RHE and 19.31 mV dec^-1) are much smaller than those of RuO₂ (1.557 V vs RHE and 64.03 mV dec^-1). For full water splitting, the catalytic current density achieves 10 mA cm^-2 at a low cell voltage of 1.584 V for the (-) Ni@BNPCFs-900||Ni@BNPCFs-900 (+) electrolysis cell, which is 10 mV smaller than that of the (-) 20 wt % Pt/C||RuO₂ (+) benchmark (1.594 V) under the same conditions. The synergistic effects of 3D hierarchically porous structures, advanced charge transport ability, and abundant active centers [such as Ni@BNC, BC₃, pyridinic-N (pyridinic-N-Ni), and graphitic-N] are responsible for the excellent water-splitting catalytic activity of the Ni@BNPCFs-900 networks. Especially, because of the remarkable structural and chemical stabilities of 3D hierarchically porous Ni@BNPCFs-900 networks, the (-) Ni@BNPCFs-900||Ni@BNPCFs-900 (+) water electrolysis cell displays an excellent stability.

Electronic regulation of a core–shell NiSe2 catalyst by Co doping to accelerate hydrogen evolution

A Co-doping core–shell shaped NiSe2 based catalyst (NixCo1−xSe2@NC) exhibits promising electrocatalytic activity for HER with a low overpotential of −143 mV at −10 mA cm−2, a small Tafel slope of 37.5 mV dec−1.

Regulation of Morphology and Electrochemical Properties of Ni0.85Se via Fe Doping for Overall Water Splitting and Supercapacitor

The Fe-doped Ni0.85Se nanosheets array on Ni foam was synthesized successfully through one-step solvothermal method as effective binder-free multifunctional catalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), overall...

Self-supported and defect-rich CoP nanowire arrays with abundant catalytic sites as a highly efficient bifunctional electrocatalyst for water splitting

In 1.0 M KOH, p-CoP/NF shows outstanding HER and OER activity. Furthermore when p-CoP/NF is assembled into a two-electrode cell, a voltage of only 1.55 V is needed to achieve 10 mA cm−2, and it can maintain long-term stability.

Motivating borate doped FeNi layered double hydroxides by molten salt method toward efficient oxygen evolution

The incorporation of borate is a beneficial strategy to improve the catalytic activity of transition metal-based electrocatalyts for oxygen evolution reaction (OER). However, how to efficiently introduce borate has always been a challenge. Here, a facile and scalable molten salt method is developed to successfully dope borate into FeNi layered double hydroxides (FeB_i@FeNi LDH) for efficient OER. The molten salt method can not only promote the formation of evenly dispersed nano-pompous FeB_i precursor, thus providing the possibility to realize the direct doping of borate and the increase of mass, charge transfer and oxygen evolution active sites in FeNi LDH, but also promote the in-situ growth of FeB_i@FeNi LDH on the conductive iron foam, improvingconductivity and stability of the material. The results indicate that the synthesized FeB_i@FeNi LDH shows enhanced OER activity by delivering current densities of 10 and 100 mA cm^-2 at low overpotentials of 246 and 295 mV and showing a small Tafel slope of 56.48 mV dec^-1, benefiting from the optimization of geometric structure of active sites as well as the adjustment of electron density by borate doping especially in the case of molten salt. In addition, the sample can maintain durability at an industrial current density of 100 mA cm^-1 for 90 h. This work provides a new way for the construction of efficient catalysts using boron doping assisted by molten salt.

Oriented and robust anchoring of Fe via anodic interfacial coordination assembly on ultrathin Co hydroxides for efficient water oxidation

The oriented distribution and strong bonding of Fe active sites in multiple metal hydroxides are crucial to modulate activity and stability for efficient oxygen evolution reaction (OER). However, the dispersion and inevitable dissolution of Fe species still need to be addressed through deliberate design. Here, trace amounts of Fe chelated with tannic acid (TA) are precisely anchored to ultrathin Co hydroxides (TF@Co(OH)₂-t) through a new anodic interfacial coordination assembly strategy: firstly, the ZIF-67@Co(OH)₂ precursor with ultrathin Co(OH)₂ nanosheets vertically grown on the shell, provides abundant active sites and sufficient anchoring regions for subsequent TA-Fe coating; secondly, the TA-Fe ligand network quickly and robustly coats the surface of the Co(OH)₂via positive potential-driven chronopotentiometry, yielding TF@Co(OH)₂-t with good dispersion and controllable Fe species. The TA-Fe network efficiently activates Co species and prevents the dissolution of Fe ions. Physical characterization and DFT simulations reveal that the optimized OER activity with 317 mV at 10 mA cm^-2 for TF@Co(OH)₂-500 can be attributed to the accelerated electron transfer, increased active sites, and the moderate fall in d-band center levels due to Fe integration. Moreover, prolonged stability is realized benefiting from the robust TA-Fe coating protecting the actives sites.

Self-supported nickel-doped molybdenum carbide nanoflower clusters on carbon fiber paper for an efficient hydrogen evolution reaction

Developing an efficient, stable and low-cost noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER) is an effective way to alleviate the energy crisis. Herein, we report a simple and facile approach to synthesize self-supported Ni-doped Mo₂C via a molten salt method. By optimizing the content of Ni, the concentration of Ni(NO₃)₂, and the annealing time, self-supported nanoflower-like electrocatalysts composed of ultrathin nanosheets on carbon fiber paper (CFP) can be achieved. Such a fluffy and porous nanoflower-like structure has a large specific surface area, which can expose many active sites, and promote charge transfer; moreover, all of the above is beneficial for improving the HER performance. Density functional theory (DFT) calculations reveal that the doping of Ni leads to a down shift of the value of the d band center (ε_d), so that the adsorbed hydrogen (H_ads) is easier to desorb from the catalyst surface, thus leading to an enhanced intrinsic catalytic activity of Ni doped Mo₂C based catalysts. As a result, Mo₂C-3 M Ni(NO₃)₂/CFP with a nanoflower-like structure prepared at 1000 °C for 6 h exhibits the best electrocatalytic performance for the HER in 0.5 M H₂SO₄, with a low overpotential of 56 mV (at j = 10 mA cm^-2) and a Tafel slope (27.4 mV dec^-1) comparable to that of commercial Pt/C (25.8 mV dec^-1). The excellent performance surpasses most of the noble-metal-free electrocatalysts. In addition, the outstanding long-term durability of Mo₂C-3 M Ni(NO₃)₂/CFP is demonstrated by showing no obvious fluctuations during 35 h of the HER testing. This work provides a simple and facile strategy for the preparation of nanoelectrocatalysts with high specific surface areas and high catalytic activities, both of which promote an efficient HER.

Boron carbonitride with tunable B/N Lewis acid/base sites for enhanced electrocatalytic overall water splitting

In-depth research on energy storage and conversion is urgently needed; thus, water splitting has become a possible method to achieve sustainable energy utilization. However, traditional carbon material with high graphitization degree exhibits a relatively low electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity as it is electrochemically inert. In this work, according to the Lewis theory of acids and bases and the density functional theory (DFT) results, which show that the enriched heteroatom of B/N in the boron carbonitride (BCN) system may introduce stronger adsorption strength of OH*/H₂O, respectively, we have designed and synthesized self-supporting BCN materials with different enrichment degrees of B/N (B-BCN/N-BCN) using carbon paper as substrate. Furthermore, by adjusting the contents of B and N, the optimum electrocatalytic performance of overall water splitting was obtained in which the onset voltage of water splitting on B-BCN//N-BCN was lower than 1.60 V. Our strategy of synthesizing materials with different heteroatom enrichment to improve the electronic environment of materials has opened up new opportunities for developing efficient metal-free electrocatalysts.

Metal-Organic Framework-Derived NiS/Fe3O4 Heterostructure-Decorated Carbon Nanotubes as Highly Efficient and Durable Electrocatalysts for Oxygen Evolution Reaction

Because of the sluggish oxygen evolution kinetics, it is extremely important but still challenging to develop low-cost, efficient, and stable electrocatalysts for oxygen evolution reaction (OER) to enhance the efficiency of water electrolysis. Herein, for the first time, we present a novel heterostructure catalyst, constructed by ultrafine NiS/Fe₃O₄ heterostructural nanoparticles decorated on a carbon nanotube (CNT) matrix (NiS/Fe₃O₄ HNPs@CNT), which is synthesized by a facile hydrothermal reaction and subsequent sulfurization process. The NiS/Fe₃O₄ HNPs@CNT hybrid delivers superior OER activity in alkaline medium: it delivers a current density of 10 mA cm^-2 at an ultralow overpotential of 243 mV with a small Tafel slope of 44.2 mV dec^-1, which outperforms the benchmark RuO₂ electrocatalyst; moreover, it exhibits terrific long-term stability over 36 h without any noticeable performance decay. The exceptional OER performance can be attributed to the unique nanoarchitecture, high conductivity of the CNT matrix, and particularly, the interaction between the Ni and Fe species in NiS/Fe₃O₄ heterostructural nanoparticles. This work introduces a sensible nanoarchitecture design with a facile and novel fabrication strategy to attain nonprecious metal-based composite catalysts with high OER performance and outstanding long-term stability.

The one-pot synthesis of porous Ni0.85Se nanospheres on graphene as an efficient and durable electrocatalyst for overall water splitting

Ni_0.85Se/RGO composite exhibits extraordinary water splitting.